#157 added a second isImageAvailable-method which uses HEAD instead of GET in VermessungRissReportScriptlet
#157 use that alternative method in VermessungRissAggregationRenderer
#157 added a benchmark test to compare the both methods
#157 removed VermessungRissReportScriptletTest
#157 in VermessungRissEditor.tryToLoadImageFromURLs() use the WebAccessManager.checkIfURLaccessible() to check if an URL exists. This can be done because the content of the URL is acutally not used.
#157 in VermessungRissReportScriptlet.isImageAvailable() use WebAccessManager.checkIfURLaccessible() instead of writting that logic itself. Furthermore a HEAD request is used to check if the URL is available.